The renal handling of
ceftazidime was studied in 8 patients with
cystic fibrosis and 10 healthy controls. The renal clearance of
ceftazidime (CLRcz) was measured after an intravenous single dose and during low and high plasma concentration steady-state infusions. The glomerular filtration rate (GFR) was simultaneously estimated by
inulin clearance (CL inul). The average CLRcz (mean +/- SD) was higher in
cystic fibrosis patients (125 +/- 20 ml/min/1.73 m2) than in healthy controls (100 +/- 9 ml/min/1.73 m2) [p less than 0.005]. Also CL inul (mean +/- SD) was increased in
cystic fibrosis patients (132 +/- 30 ml/min/1.73 m2) compared with healthy controls (103 +/- 8 ml/min/1.73 m2) [p less than 0.02]. The mean renal clearance ratios of
ceftazidime to
inulin were close to unity after both the single dose and low and high dose steady-state infusions both in
cystic fibrosis patients and in controls. These findings suggest that the glomerular filtration rate is the principal determinant of the elimination rate of
ceftazidime. However, in all
cystic fibrosis patients with a CL inul exceeding 125 ml/min/1.73 m2 the clearance ratio was below unity, indicating tubular reabsorption of
ceftazidime occurs in these individuals. The results demonstrate a higher but also more variable GFR in
cystic fibrosis patients (74 to 174 ml/min/1.73 m2), resulting in increased and accordingly variable ability to eliminate
ceftazidime in
cystic fibrosis. However, these pharmacokinetic changes are not large enough to call for special dosage considerations for
ceftazidime in
cystic fibrosis.